The known method for obtaining a gas containing a high concentration of an adsorbable gas by subjecting a gas (hereinafter referred to as an original gas) containing a low concentration of the adsorbable gas to adsorption using an adsorbent and then desorbing the adsorbable gas adsorbed by the adsorbent by heating consists of having the adsorbable gas adsorbed by the adsorbent by passing the original gas from one side of a bed packed with the adsorbent to the other side of the bed and then indirectly heating the adsorbent from outside the packed bed, followed by desorbing and recovering the adsorbable gas either by introducing a heated carrier gas in contact with the adsorbent or by introducing a carrier gas having a temperature higher than that of a usual heated carrier gas in contact with the adsorbent.
In the conventional method, the maximum concentration rate which can be achieved by one cycle of adsorption and desorption is only about 10-20 times for a usual temperature of heating. Moreover, since only a small amount of a carrier gas can be used during desorption in order to obtain a recovery gas of high concentration, the gas flow rate in the adsorbent bed becomes low thereby resulting in nonuniform flow and insufficient heating.